1. Field of the Invention
The present invention relates to a drive apparatus for moving a certain object (driven object) in a desired direction.
2. Description of the Prior Art
An example of the prior art having this type of drive apparatus is the XY table indicated in FIG. 1.
As indicated in FIG. 1, said XY table is comprised of X table 1 installed on the floor or a mounting frame in a workshop, and Y table 2 moved by said X table 1. Furthermore, since X table 1 and Y table 2 mutually have nearly the same constitution, the following detailed explanation will be provided with respect to X table 1 only, and an explanation of Y table 2 omitted. However, those constituent members of Y table 2 that correspond to the constituent members of X table 1 are indicated using the same reference numerals. Furthermore, an exploded view of the constituent members of X table 1 divided into suitable blocks is indicated in FIG. 2.
As indicated in FIG. 1, X table 1 has a long, roughly rectangular plate-shaped base 5, and side plate 6, provided on said base 5 and forming a box with said base 5. Motor 7 is mounted on one end of this side plate 6. In addition, as is indicated in FIG. 2, pulley 9 is fit onto output shaft 7a of motor 7. In addition, another pulley 10 is arranged on base 5, and is mounted to base 5 by means of brackets not shown. Endless belt 12 is wrapped around pulleys 9 and 10. A driven object in the form of moving table 13 is fastened to this belt 12.
As indicated in the drawings, moving table 13 has a prescribed thickness and is composed to be of a size that allows it to be contained within the width of side plate 6. Two table projections 13a projecting above the upper surface of side plate 6 are provided in parallel on the left and right sides. These table projections 13a may be formed into an integrated structure with moving table 13 or may be composed in the form of separate structures. Above-mentioned Y table 2 is mounted on the upper surface of said table projections. Furthermore, cover 15 is arranged to the inside of these table projections 13a, acting to prevent entrance of dust and so on.
A driving device that drives belt 12 is comprised of the above-mentioned motor 7, pulley 9 and pulley 10.
On the other hand, as is indicated in FIG. 2, a pair of linear motion rolling guide units 17 are mutually arranged in parallel on the right and left sides of the above-mentioned belt 12, and are mounted on base 5. These linear motion rolling guide units 17 receive the load in all four directions (the directions indicated by arrows Z and Y as well as their respective opposite directions) applied to moving table 13, and also act as guiding devices that guide moving table 13. The driving apparatus that moves moving table 13, the driven object, is composed of these linear motion rolling guide units 17 and the above-mentioned belt 12 and its driving device.
More specifically, linear motion rolling guide unit 17 is composed of track rail 18, roughly in the shape of a square column, in which track groove 18a, having a semi-circular cross-section, is formed in the left and right shoulders of the side wall, and slider 20, which is guided by said track rail 18. In addition, this slider can slide relative to track rail 18 being straddled across said track rail 18. Said slider 20 also has casing 20a, in which track grooves (not shown), having a semi-circular cross-section, are formed in the inside surface so as to oppose track grooves 18a of said track rail 18, a plurality of balls (not shown) that roll over a track path formed by both said track grooves in relative motion, and end caps 20b mounted on both ends in the lengthwise direction of said casing. Furthermore, linear motion rolling guide units 17 are not limited to the use of balls, but may also use other devices such as rollers as long as they are of a constitution that uses a rolling object.
The following provides an explanation of the operation of the XY table having the above-mentioned constitution. Furthermore, since X table 1 and Y table 2 have the same constitution as described above, the following explanation will deal primarily with X table 1.
Firstly, when a power voltage is supplied to motor 7 of X table 1, output shaft 7a of motor 7, serving as the driving source, rotates which transmits torque to pulley 9. Then, belt 12, wrapped around pulley 9 and pulley 10, is driven in a prescribed direction, and moving table 13, mounted on the upper surface of this belt 12, also moves guided by linear motion rolling guide units 17. Conversely, when the direction of rotation of motor 7 is reversed, belt 12 is driven in the opposite direction from that above, and consequently, moving table 13 also moves in that direction. In addition, the movement of moving table 13 is controlled by a control circuit composed of a microcomputer and so on. A detector, which outputs a position detection signal to this-control circuit, is composed to be able to be mounted to the inside of side plate 6 indicated in FIG. 1, and on the upper surface of base 5. In addition, detection may also be performed by an encoder mounted behind motor 7.
In addition, since Y table 2 is mounted on table projections 13a of moving table 13 equipped on X table 1, it moves in the X direction which is the same direction as moving table 13 of X table 1. As moving table 13 of Y table 2 is composed so as to be able to independently move linearly in the Y direction, by controlling these with a control circuit not shown, moving table 13 of Y table 2 can be moved in both the X and Y directions.
FIG. 3 indicates the drive apparatus of a second example of the prior art. This drive apparatus can be incorporated into the XY table indicated in FIG. 1 in the same manner as the drive apparatus of the first example of the prior art indicated in FIG. 2.
As indicated in FIG. 3, said drive apparatus has long ball screw 26, provided in parallel with track rail 18 equipped with linear motion rolling guide unit 17, and attached at both ends to base 5 by means of support bearings 25, motor 27 that rotates said ball screw 26, and nut 28 engaging with ball screw 26 and mounted with respect to moving table 13, the driven object.
Furthermore, since the drive apparatus indicated in FIG. 3 is composed in the same manner as the first example of a drive apparatus of the prior art indicated in FIG. 2 with respect to portions other than those described above, an explanation of the entire apparatus will be omitted. In addition, in the above-mentioned explanation, the same reference numerals are used for those constituents that are identical to the constituents equipped on the first example of the prior art.
In said second example of a drive apparatus of the prior art, when ball screw 26 is driven to rotate by motor 27, moving table 13 moves together with nut 28.
As described above, in addition to linear motion rolling guide unit 17 for guiding of the driven object, the drive apparatus of the prior art has long components for transmission of driving force, such as belt 12 or ball screw 26, motors 7 and 27, that serve as the driving source, and several other peripheral components, such as pulleys and bearings, related to these. Accordingly, this drive apparatus has the shortcomings of being large in size and having a large number of components resulting in high costs. In addition, since the driving force produced by motors 7 and 27, serving as the driving sources, is transmitted through numerous members, such as long components, for transmission of driving force, this drive apparatus has the additional shortcoming of it being difficult to attain a high degree of accuracy in movement and positioning of the driven object. Moreover, together with it not always being easy to attain high-speed driving with this drive apparatus, due to the large number of components operating relative to each other, this drive apparatus has the shortcoming of producing a relatively high level of noise. In the case of using the above-mentioned belt 12 in particular, since said belt becomes stretched due to application of torque, together with positioning accuracy being poor, there is also the shortcoming of dust and debris being produced from said belt 12. In addition, in the case of the above-mentioned ball screw 26, since deflection of the screw shaft occurs when this is excessively long, sliding characteristics become unstable.